An extensive literature review of published research located 61 corn trials (representing 687 site-years of data) that compared corn yields by tillage system. All of the trials summarized used a close variant of a true no-tillage system with minimal surface disturbance only at planting and/or during fertilizer application. The conventional tillage systems varied from a maximum of fall moldboard plowing followed by multiple spring tillage passes to a minimum of fall chisel plowing followed by one or more spring tillage operations prior to planting. Strip tillage was not included because there were very few published studies on strip-till, and the methods varied too widely to make valid comparisons.
These trials were then mapped to look for geographic and environmental patterns in the relative performance of no-tillage vs. conventional fall tillage on corn yield. An economic analysis was not attempted because many of the studies did not provide enough information for such an analysis, and because the economics of tillage vary by many factors.
The national average difference in yield between no-tillage and conventional tillage corn was negligible with a small 0.5% yield advantage for conventional tillage (Table 1). However, the plot of corn experiment locations clearly shows regional differences in tillage effect on yield
Table 1. Corn yield advantage of no-till over conventional tillage.
A number of observations were collected during the analysis of the existing literature on tillage effects on soybean yield. Several studies indicated no-tillage yields improve after several years of continuous no-till have been in place. This time effect was thought to be the result of improved soil tilth over time in the no-tillage plots caused by increases in organic matter, soil enzyme activity, microbial biomass, and changes in soil porosity and aggregation. Drainage in new no-tillage plots is often poor until old tillage pans and lack of soil structure is corrected over time. Experiments conducted for a short number of years (less than 4 or 5) without prior years of no-tillage in the no-till plots probably do not provide a completely fair comparison to conventional tillage because the no-till soils have not had time to stabilize.
It seems clear from this summary that the most important factor governing the success or failure of no-till compared to conventional tillage is soil moisture. No-till provides greater yields in the eastern, southern, and western United States where high temperatures, soils with low water-holding capacity, and/or unfavorable rainfall patterns often cause drought stress. No-till yields are equal or slightly less than conventional tillage in the northern United States and Canada where cold, wet spring conditions and poorly drained soils cause slower emergence and crop development in short maturity zones.
The tillage regions outlined in this review do not have absolute or rigid boundaries. There are pockets of well-drained soils and local climate in the north where no-till works very well, and areas with poorly drained soils and local climate conditions in the south and west where no-till is more challenging. However, the general boundaries and trends are reasonably clear.
Over 40% of soybeans in the United States are now produced using no-tillage practices. It is apparent from this summary that a majority of the soybean producing regions of the U.S. would see a yield benefit or at least no yield reduction from no-tillage production. Even in the northern region the yield penalty to no-till soybeans is often more than out-weighed by the labor and fuel reductions and improvements in soil quality and conservation.
¹Note: This Crop Insights is based on the recently published journal article: DeFelice, M. S., P. R. Carter, and S. B. Mitchell. 2006. Influence of Tillage on Corn and Soybean Yield in the United States and Canada. Online. Crop Management. doi:10.1094/CM-2006-0626-01-RS. ©2006, PMN.